Okla. Stat. tit. 68, § 2374

In the case of any refund to a taxpayer as provided in Section 226 of the Uniform Tax Procedure Code for taxes collected pursuant to this act, the Tax Commission shall pay interest thereon at the rate of six percent (6%) per annum from the date of payment by the taxpayer to the date of such refund. To the extent inconsistent herewith, Section 226 of the Uniform Tax Procedure Code is hereby superseded.